You enquire about the mode of goodness, and why such people do not worship Krishna. Actually, this is not the final stage, one has to go further ahead to suddha sattva. In the material mode of goodness there are sometimes tinges of the modes of passion and ignorance, but in the suddha sattva stage there is only pure love of God or pure mode of goodness, that is the difference.
Regarding Sandipani Muni, he got knowledge from his Spiritual Master, but there is no mention who he is.
Krishna Prasad is always all right. The consideration of spoiling foodstuff after 3 hours, that is ordinary or it is so for persons who are not advanced in accepting Krishna prasada as transcendental, just like Ragunatha Goswami: he was collecting rejected rice from the cooking of Lord Jagannatha and he was eating only that. So this is a higher stage, so for the time being you should know that Krishna prasada is never contaminated by any material source.
Now I am pleased that you are making serious study of this our Krishna philosophy, so I want that you go on like this until you will able to defeat any challenge from atheists and rascals, then your preaching work will have real potency and combinedly with your Godbrothers around the world and at London Temple you shall preach so strongly that one day this Krishna consciousness movement will change the world from the most dangerous condition; that is the wish of Lord Caitanya Mahaprabhu, and tomorrow we shall be celebrating the Lord's Appearance Day by laying down the corner-stone for our World Headquarters here at Mayapur.